Electrode cap



R. M. HEINTZ Aug.- 21, 1934.

ELECTRODE CAP Filed July 18 1952 INVENTOR, RALPH M. HE/N TZ.

ATTORNEY Patented Aug. 21, 1934 PATENT OFFICE ELECTRODE CAP Ralph M. Heintz, Palo Alto, Calif., assignor' to Heintz & Kaufman, Ltd., San Francisco, Calif.,

a corporation of Nevada Application July 18, 1932, Serial No. 623,137

1 Claim.

. My invention relates to a connection cap for an electrode sealed through the envelope of a thermionic tube, and more particularly to a cap which will greducethe danger of envelopepunc- ,:ture ,when used with gaseous discharge devices, such as mercury vapor rectifiers,- neon'tubes, or

. the like.

Among the objects of my invention are: to provide a cap for an electrode sealed through 0 an envelope of a gaseous discharge tube which Will reduce dielectric stresses in the envelope ad- .jacent the-cap; to provide a cap for an electrode arm of a thermionic tube which will minimize corona discharge, between the cap and the envelope; to provide a heat retaining connection cap for an electrode sealed through the envelope of an electrical discharge tube containing mercury vapor, which will prevent the condensation of mercury in liquid phase in the envelope ad- 0 jacent the cap; to provide a heat retaining cap for an electrode having a polished surface to diminish heat radiation; and to provide a cap for an electrode sealed into an envelope, having a dead air space between the envelope and the cap.

Other objects of my invention will be apparent or will be specifically pointed out in the description forming a part of this specification, but I do not limit myself to the embodiment of 0 my invention herein described, as various forms may be adopted within the scope of the claim.

The drawing shows a sectional view of an envelope arm with the cap of my invention in position, the electrode being shown in elevation.

In gaseous discharge devices containing a filling of the monatomic gases, such as neon, helium, mercury vapor and the like, at reduced pressures, it is customary to extend a tubular projection or arm from the envelope. The electrode support is sealed through the distal end of this arm,

and the electrode mounted thereon.

In order to protect the end of the projection and the seal, a cap, fitting closely over and enclosing the end of the tube, is often cemented M in place, and used for an electrical contact, the

electrode support being soldered or welded to this cap.

Due to the fact that the inner surface of such tubes accumulates a charge, excessive dielectric 0 stresses are set up in the envelope adjacent the cap. Many cases of tube failure are due to envelope puncture at the point of stress.

Furthermore, when such caps are used on anode arms energized to a high voltage, the rim 5 of the cap, being close to the envelope, initiates .charge device.

a corona discharge. This corona, playing over the glass, locally strains and soon weakens it, a circular ring crack adjacent the rim occurs, and the arm breaks off at that point.

In tubes using mercury vapor as the gaseous qo filling, such caps tend to cool the arms by heat radiation. Such cooling allows the mercury to condense in liquid phase within the arm or projection, and the presence of liquid mercury in the arm is highly objectionable. 5

Broadly speaking, my invention comprises a cap which has a cup-shapedv portion adapted to fit over the exposed end of anelectrode arm extended from the .envelope of an electrical dis- The rim of the cup is turnedinwardly to form a bead, which when the cap is positioned on the arm, contacts the envelope and holds the remainder of the cap away from the walls of the arm. A minimum amount of cement is used to fix the cap in place, and a dead air space is thus formed which insulates the enclosed portion of the arm from the cupshaped portion of the cap.

The outer surface of the cap is highly polished to further minimize heat radiation, and the usual go electrical connection is made between electrode support and the cap.

A preferred embodiment of the invention is shown in the drawing. The envelope 1 of a thermionic or gaseous discharge device has extended, therefrom a tubular projection or arm 2. Fused to the distal end of the arm is areentrant stem 4, having an electrode support 5 sealed through at 6. This seal may be provided with a protecting sleeve 7 as has been disclosed in the copendgo ing application of William W. Eitel and Frederick J. Schack, Serial No. 612,948, filed May 23, 1932. Electrode 8 is mounted on the support, as described in the above mentioned application.

Envelope 1, stem 4, and sleeve '7 are preferably formed from a heat resistant glass such as that known in the trade as Pyrex, G702P, or others of like characteristics.

The device is assembled and evacuated in the usual approved manner, and a connection cap,, 9, of brass or other easily worked material, is placed over the electrode arm. This cap has a cup-shaped portion 10, and the rim is inturned to form a bead 11. While it is desirable to bury the cut edge 12 of the rim, as shown, it is on1y necessary to turn the edge enough to be away from the envelope when applied, and the bead thus formed should be of substantially circular cross section.

While the cap is being placed over the end of 116 the arm, the electrode support enters a hole in the boss 14 and is welded, soldered or otherwise fastened to the cap as shown at 15. The entire cap is preferably provided with a polished surface 16.

Other methods of joining the cap to the electrode support and other shapes of the boss 14 may be desirable, and the particular means shown is no part of my invention.

In mounting the cap on the arm a minimum amount of cement 17 is applied, leaving a dead air space 18 completely surrounding the end of the electrode projection.

It is to be understood that the cap of my invention may utilize one or more of its distinctive features in accordance with the type of thermionic tube on which it is mounted. In devices having no gaseous content, the cap may be used at high voltages, and will greatly reduce corona discharge because of the rounded edge presented to the glass. The rough edge of the metal being turned away from the glass envelope cannot cause a brush discharge on to the glass, and so eventually crack it.

In devices containing monatomic gases in vapor phase at ordinary temperatures, such as neon or helium, corona discharge will be reduced, and field concentrations due to charges accumulating beneath the cap will be rendered harmless because of the narrow edge of the bead contacting the envelope, and by the fact that the bead presents a continuously curving surface to the glass, thereby tending to shade oiT dielectric stresses in the glass, and prevent puncture.

When mercury vapor is used in devices such as rectifiers, not only are the above described features in operation, but also there is a distinct advantage to be gained by utilizing the heat retaining characteristic of the cap. It is known that the vapor pressure of mercury in the entire tube is dependent on the temperature of the coldest part of the tube, and when tubes are designed for certain operating pressures, condensation of mercury in electrode arms will upset the proper operation of the tube, by changing the vapor pressure.

In addition, globules of mercury around an anode arm operating at a voltage of 10,000 to 15,000 volts with respect to a cathode, are apt themselves to accumulate a charge sufiiciently high to puncture the glass, if adjacent the electrode cap. By providing a dead air space between the cap and the end of the arm, and by polishing the cap to slow down heat radiation, I am able to maintain the end of the arm at a temperature sufiiciently high to prevent mercury condensation in that locality.

I claim:

In combination with an electrode sealed into an envelope containing a conductive gas, an exterior connection cap having a cup-shaped portion and an inturned rim of substantially circular cross section, said cup-shaped portion being spaced away from said envelope, and said inturned rim presenting a continuously curved surface to said envelope whereby excessive field concentrations between said cap and said gas are prevented.

RALPH M. HEINTZ. 

